Materials

What is density

Density is how compact an object is

what is the formula for density

mass/ volume

What are the unit for density

kg/m³

How does density of a object determine if it floats or sinks in a fluid

solid object will float in liquid if it density is lower than that of the liquid

what is the density of water

1g/m³

What is hooke’s law

Extension is proportinal to the force applied

F= ke where k is springs constant

What are the units for springs constant

N/m

What is limit of proportionality

The limit beyond which hooke’s law is no longer obeyed

graph starts to curve

WHat is the elastic limit

If you exceed this limit object won’t return to original lenght after its unloaded

Deformation

Force expericed by object cause change in shapt

• tensile forces strech the shap

• compressive forces compress the shape

What is elastic deformation

Material can still return to original length once unloaded, below elastic limit

What is plastic deformation

Material can’t still return to original length once unloaded

Why does plastic deformation happen

when force is applied some atom in material move positions relative to one another when the load is removed they don’t return to their original space

What from is the energy transferred to when elastically stretched or compressed

elastic strain energy = into kinetic or thermal energy

What from is the energy transferred to when plastically stretched or compressed

work is done to separate atoms so energy is stored in elastic strain energy

How does plastic deformation help in car crashes

Energy is transferred to change the shape of the vehicle rather than to the person

How do you calculate extension in parallel spring

extension in string/ number of springs

How do you calculate extension in parallel spring

F=nkL

How do you calculate extension in series spring

number of springs* extension of 1 spring

How do you calculate k in parallel spring

k1+k2 +k3…..+kn=Kt

How do you calculate k in series spring

1/k1 +1/k2 1/k3 +…..= 1/Kt

what does the area under force extenstion graph represnt

work done to strech/ compress= elastic strain enrgy

What is elastic strain energy

Ep+ thermal energy

What is stress defined as

force applied / crossedtional area

What are the units for stress

Pa or Nm^-2

What is strain

change is lenght / original lenght

What are the units for strain

no units as its a ratio

What happens at breaking point

the stress on material is so greate heat is causes the atoms to be pulled apart unitl they are sperated completly and material breaks

What is UTS

maximum stress a material can withstand - after this point no more extra force is applied but object will keep extending

What do can affect breaking point and UTS

temperature

What is young’s modulus

Its a measure of stifness

What does the gradient of stress strain graph show

Youngs modulus but only till stress is proportional t strain

What does the area under stress strain graph represent

Elastic strain energy per unit volume

What does ductile mean

how easy it is to draw out a material into a wire

what does brittle mean

object that break without bending or steching much

What is Yield point

- material suddenly starts to strech without extra load

What is the diffrence between force extension graphs vs stress strain graph

• force extension graph are specifice to object

• stress strian graph are specific to material